Wagner mechanism

Figure 11-11. Displacement reactions of the type AX+BY = AY+BX. a) lost mechanism, schematic, b) Equipotential surfaces and the evolution of phase boundary instability, lost mechanism, c) Wagner mechanism of displacement reactions, schematic.

For the very simplified situation that the sphere behaves electrically as a pure capacitor, and the solution as a pure resistance, the relaxation can be described by a Maxwell-Wagner mechanism, with T = e e/K, see (1.6.6.321. Although some success has been claimed by Watillon s group J to apply this mechanism for a model, consisting of shells with different values of e and K, generally a more detailed double layer picture is needed. In fact, this Implies stealing from the transport equations of secs. 4.6a and b. generedizing these to the case of a.c. fields. 

However, 0 ion diffusion is not very common. Due to their larger ionic radius, 0 ions are expected to have a considerably lower mobility than most cations. When cations are the only transporting species, the mechanism is known as the Wagner mechanism (Wagner, 1936). Formation of the spinel phase can be easily explained by diffusion of Mg " and counter-diffusion of AP". To maintain electro-neutrality, the mechanism involves the counter-diffusion of three Mg " ions for every two Al ions (Carter, 1961). 

A more complete test of the Wagner mechanism and treatment has been carried out by Fueki and Wagner and by Mrowec and Przybylski who derived values for the diffusion coefficient of nickel in NiO and cobalt in CoO from measurements of the parabolic oxidation rate constant. Since the parabolic rate constant can be expressed in the form of Equation (3.48),... 

M.M. Hassan, M. Mueller, D.J. Tartakowska, and D.H. Wagner, Mechanical performance of hybrid rice straw/sea weed polypropylene composites. J. Appl. Polym. Sci. 120, 1843-1849 (2011). 

Wagner (1961) examined theoretically the growdr kinetics of a Gaussian particle size distribution, considering two growth mechanisms. When the process is volume diffusion controlled... 

A mechanism for formation of the first product by Wagner-Meerwein rearrangement has been proposed. ... 

Wagner, J., Lerner, R. A., and Barbas, C. F., Ill, 1995. Efficient adolase catalytic antibodies that use tlie enamine mechanism of natural enzymes. Science 270 1797-1800. See also tlie discussion entitled Aldolase antibody in Science 270 1737. 

Ruach-Nir I, Wagner HD, Rubinstein I, Hodes G (2003) Structural effects in the electrodeposition of CdSe quantum dots on mechanically strained gold. Adv Eunct Mater 13 159-164... 

In some cases, the oxide-coating protects the surface from further oxide buildup. One example is that of aluminum where an oxide coating appears almost instantaneously once the pristine surface is exposed to air. Yet, there are many cases where the oxide layer continues to buildup until the metal is totally consumed (One example is that of iron and "rust"). How is this possible Wagner hypothesized that both metal and oxide ions difiosed through the metal oxide layer so as to build up the layer thickness from both sides. The following diagram is one representation of such a mechanism ... 

Wagner, U.G., Hasslacher, M., Griengl, H. et al. (1996) Mechanism of cyanogenesis the crystal structure of hydroxynitrile lyase from Hevea brasiliensis. Structure (London, England 1993), 4, 811-822. 

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